I checked this out on my Mara, you can see there is more to this bug than just the butt area. If you look at the legs of my char they are miss colored. This reminds me quite a bit of the Relaxed Vestment's bug. If its the same type of issue good luck ever seeing this fixed.
Someone identified the problem. The colors on the legs of the female toons are reversed so the knee is on the rear of the legs and the hip rip is caused by the fact that it is the front side we see from the rear.
So yes it is a bug, I just fear it will take 6 months for them to get around to fix it.